The present invention relates to a toner produced by attaching fine particles to a base particle and a manufacturing method of the toner, and more particularly relates to a toner necessary for an electrophotographic technique used in image forming apparatuses such as copying machines and printer machines and a method of manufacturing the toner.
Image forming apparatuses such as copying machines and printer machines use an electrophotographic technique in which an image is formed by uniformly charging a photosensitive drum, forming an electrostatic latent image on the charged photosensitive drum by scanning an optical image based on the image to be formed, performing development to turn the formed electrostatic latent image into a visible image by attaching a powder toner containing a colorant to the electrostatic latent image, transferring the obtained visible image onto a sheet such as copy paper, and fixing the transferred toner to the sheet.
Typical examples of a method of fixing a toner to a sheet include a heat fixing method in which a toner is fixed to a sheet such as copy paper by heating and melting the toner; and a pressure fixing method in which the composition of a toner is deformed by pressing the toner, and the toner is fixed to a sheet. As the heat fixing method, from the point of view of simplicity of the machine and the quality of images after fixed, a heat roll fixing method using a heat roll as a heating medium for heating the toner is the most popular method. In the heat fixing method, it is necessary to fix the toner onto a sheet by melting the toner at a low temperature. In particular, there is high demand for low-temperature fixing ability of the toner from the point of view of saving energy in recent years, and the demand for low-temperature fixing ability is satisfied by lowering the softening temperature by decreasing the molecular weight of a resin contained in the toner and adding a wax.
However, although the method including decreasing the molecular weight of the resin and adding a wax has the advantageous effect on the low-temperature fixing ability, it has problems of deterioration of storage stability and durability during long-time running. Therefore, various methods have been proposed to satisfy both the low-temperature fixing ability and the storage stability and durability by attaching fine particles to the surface of a base particle that becomes a toner.
As one of these methods, there is disclosed a method in which non-cross-linked type organic fine particles manufactured by a soap-free emulsion polymerization method are externally added (for example, Patent Document 1: Japanese Patent Application Laid-Open No. 60-186854/1985). Moreover, there is disclosed a method in which non-cross-linked type organic fine particles having a core-shell structure are externally added (for example, Patent Document 2: Japanese Patent Application Laid-Open No. 9-281742/1997). Further, there is disclosed a method in which fine particles having the opposite polarity to the surface of the base particle are electrically attached (for example, Patent Document 3: Japanese Patent Application Laid-Open No. 64-59239/1989, and Patent Document 4: Japanese Patent Application Laid-Open No. 2-105162/1990).
However, the toners manufactured by the methods shown in Patent Document 1 and Patent Document 2 have the problem of insufficient durability, and, if the amount of addition of the fine particles is increased to solve the problem associated with durability, there arises the problem that the oozing effect of wax in oil-less fixing is reduced and the offset resistance is decreased.
Further, the toners manufactured by the methods shown in Patent Document 3 and Patent Document 4 have the problem of deterioration of chargeability because they have a functional group that is charged to the polarity opposite to the base particle.